[PATCH] net: Revert "fib_trie: use seq_file_net rather than seq->private"

[PATCH] net: Revert "fib_trie: use seq_file_net rather than seq->private"

[Sasha Levin]

This reverts commit 30f38d2fdd79f13fc929489f7e6e517b4a4bfe63.

fib_triestat is surrounded by a big lie: while it claims that it's a
seq_file (fib_triestat_seq_open, fib_triestat_seq_show), it isn't:

	static const struct file_operations fib_triestat_fops = {
	        .owner  = THIS_MODULE,
	        .open   = fib_triestat_seq_open,
	        .read   = seq_read,
	        .llseek = seq_lseek,
	        .release = single_release_net,
	};

Yes, fib_triestat is just a regular file.

A small detail (assuming CONFIG_NET_NS=y) is that while for seq_files
you could do seq_file_net() to get the net ptr, doing so for a regular
file would be wrong and would dereference an invalid pointer.

The fib_triestat lie claimed a victim, and trying to show the file would
be bad for the kernel. This patch just reverts the issue and fixes
fib_triestat, which still needs a rewrite to either be a seq_file or
stop claiming it is.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 net/ipv4/fib_trie.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 243c7f4..5afeb5a 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -2166,7 +2166,7 @@ static void fib_table_print(struct seq_file *seq, struct fib_table *tb)
 
 static int fib_triestat_seq_show(struct seq_file *seq, void *v)
 {
-	struct net *net = seq_file_net(seq);
+	struct net *net = (struct net *)seq->private;
 	unsigned int h;
 
 	seq_printf(seq,
-- 
1.7.10.4

Re: [PATCH] net: Revert "fib_trie: use seq_file_net rather than seq->private"

[David Ahern]

On 6/4/14, 4:02 PM, Sasha Levin wrote:
> This reverts commit 30f38d2fdd79f13fc929489f7e6e517b4a4bfe63.
>
> fib_triestat is surrounded by a big lie: while it claims that it's a
> seq_file (fib_triestat_seq_open, fib_triestat_seq_show), it isn't:
>
> 	static const struct file_operations fib_triestat_fops = {
> 	        .owner  = THIS_MODULE,
> 	        .open   = fib_triestat_seq_open,
> 	        .read   = seq_read,
> 	        .llseek = seq_lseek,
> 	        .release = single_release_net,
> 	};
>
> Yes, fib_triestat is just a regular file.
>
> A small detail (assuming CONFIG_NET_NS=y) is that while for seq_files
> you could do seq_file_net() to get the net ptr, doing so for a regular
> file would be wrong and would dereference an invalid pointer.
>
> The fib_triestat lie claimed a victim, and trying to show the file would
> be bad for the kernel. This patch just reverts the issue and fixes
> fib_triestat, which still needs a rewrite to either be a seq_file or
> stop claiming it is.

It worked fine for me.

fib_triestat_seq_open() is a wrapper to single_open_net() which sets the 
namespace as the private element (returned by get_proc_net).

If CONFIG_NETNS is not set:
- single_open_net essentially sets file->private to init_net which is 
also what is returned by seq_file_net

If CONFIG_NETNS is set, all is fine.

What am I missing?

David

Re: [PATCH] net: Revert "fib_trie: use seq_file_net rather than seq->private"

[David Ahern]

On 6/4/14, 4:11 PM, David Ahern wrote:
> On 6/4/14, 4:02 PM, Sasha Levin wrote:
>> This reverts commit 30f38d2fdd79f13fc929489f7e6e517b4a4bfe63.
>>
>> fib_triestat is surrounded by a big lie: while it claims that it's a
>> seq_file (fib_triestat_seq_open, fib_triestat_seq_show), it isn't:
>>
>>     static const struct file_operations fib_triestat_fops = {
>>             .owner  = THIS_MODULE,
>>             .open   = fib_triestat_seq_open,
>>             .read   = seq_read,
>>             .llseek = seq_lseek,
>>             .release = single_release_net,
>>     };
>>
>> Yes, fib_triestat is just a regular file.

If you compare fib_trie to fib_triestat the only difference is the use 
of single_open_net and single_release_net by fib_triestat.

single_open_net is a wrapper to single_open passing struct net as the 
private data. single_open is for seq_files:


int single_open(struct file *file, int (*show)(struct seq_file *, void *),
         void *data)
{
     struct seq_operations *op = kmalloc(sizeof(*op), GFP_KERNEL);
     int res = -ENOMEM;

     if (op) {
         op->start = single_start;
         op->next = single_next;
         op->stop = single_stop;
         op->show = show;
         res = seq_open(file, op);
         if (!res)
             ((struct seq_file *)file->private_data)->private = data;

Where is the problem using seq_file_net in fib_triestat_seq_show:

static int fib_triestat_seq_show(struct seq_file *seq, void *v)
{
     struct net *net = (struct net *)seq->private;

where

static inline struct net *seq_file_net(struct seq_file *seq)
{
#ifdef CONFIG_NET_NS
     return ((struct seq_net_private *)seq->private)->net;
#else
     return &init_net;
#endif
}

David

Re: [PATCH] net: Revert "fib_trie: use seq_file_net rather than seq->private"

[Sergei Shtylyov]

On 06/05/2014 02:02 AM, Sasha Levin wrote:

> This reverts commit 30f38d2fdd79f13fc929489f7e6e517b4a4bfe63.

> fib_triestat is surrounded by a big lie: while it claims that it's a
> seq_file (fib_triestat_seq_open, fib_triestat_seq_show), it isn't:

> 	static const struct file_operations fib_triestat_fops = {
> 	        .owner  = THIS_MODULE,
> 	        .open   = fib_triestat_seq_open,
> 	        .read   = seq_read,
> 	        .llseek = seq_lseek,
> 	        .release = single_release_net,
> 	};

> Yes, fib_triestat is just a regular file.

> A small detail (assuming CONFIG_NET_NS=y) is that while for seq_files
> you could do seq_file_net() to get the net ptr, doing so for a regular
> file would be wrong and would dereference an invalid pointer.
>
> The fib_triestat lie claimed a victim, and trying to show the file would
> be bad for the kernel. This patch just reverts the issue and fixes
> fib_triestat, which still needs a rewrite to either be a seq_file or
> stop claiming it is.

> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
> ---
>   net/ipv4/fib_trie.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> index 243c7f4..5afeb5a 100644
> --- a/net/ipv4/fib_trie.c
> +++ b/net/ipv4/fib_trie.c
> @@ -2166,7 +2166,7 @@ static void fib_table_print(struct seq_file *seq, struct fib_table *tb)
>
>   static int fib_triestat_seq_show(struct seq_file *seq, void *v)
>   {
> -	struct net *net = seq_file_net(seq);
> +	struct net *net = (struct net *)seq->private;

    'void *' doesn't need any explicit casting to another pointer type, the 
cast it automatic.

WBR, Sergei

Re: [PATCH] net: Revert "fib_trie: use seq_file_net rather than seq->private"

[David Miller]

From: Sasha Levin <sasha.levin@oracle.com>
Date: Wed,  4 Jun 2014 18:02:32 -0400

> This reverts commit 30f38d2fdd79f13fc929489f7e6e517b4a4bfe63.
> 
> fib_triestat is surrounded by a big lie: while it claims that it's a
> seq_file (fib_triestat_seq_open, fib_triestat_seq_show), it isn't:
> 
> 	static const struct file_operations fib_triestat_fops = {
> 	        .owner  = THIS_MODULE,
> 	        .open   = fib_triestat_seq_open,
> 	        .read   = seq_read,
> 	        .llseek = seq_lseek,
> 	        .release = single_release_net,
> 	};
> 
> Yes, fib_triestat is just a regular file.
> 
> A small detail (assuming CONFIG_NET_NS=y) is that while for seq_files
> you could do seq_file_net() to get the net ptr, doing so for a regular
> file would be wrong and would dereference an invalid pointer.
> 
> The fib_triestat lie claimed a victim, and trying to show the file would
> be bad for the kernel. This patch just reverts the issue and fixes
> fib_triestat, which still needs a rewrite to either be a seq_file or
> stop claiming it is.
> 
> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

Thanks a lot for catching this, applied.